"Some builders don't want fuses. That's their choice. For me, I figure a fuse only comes into play when there is a problem. At that point, what do you want to lose? Just the race, or the race and the car, too?" Make certain, Overholser says, that all fuses are rated high enough to carry the load. "Don't put a 10-amp fuse where there is a 25-amp current draw," he insists. "That's just asking for trouble."
5. Don't Scrimp on Switches
He continues, "The same goes for switches. Most guys are only buying a couple of them, so the cost isn't a big deal. You probably aren't going to find what you want at the local tune-up store where you buy them for $3.99. A good aircraft quality switch will run about $15. You just shouldn't scrimp on it."
6. Crimping Isn't Enough
Don't take shortcuts on making connections, either. "Crimp all connections first," Overholser advises. "Then solder them. Then use heat shrink over the connection to really secure them. One of the problems is that most racers hold a solder gun in their hands three or four times in their lives and don't know how to use one. They get the wires way too hot and the parts get crystallized and brittle. That's no good, either."
Overholser recommends using a low-temperature solder, keeping heat to a minimum, and using just enough solder to secure the connection. It makes sense to practice a few connections before winging it with a soldering iron if you've never held one before. This practice could save you some troubleshooting grief. His company uses a heat shrink tubing that has glue inside of it to secure the wire and terminal ends.
7. Use High-Temp Wire
Wires should be rated for high-temperature use. Most of the wire found in parts houses and discount auto stores is covered by PVC-type insulation and is rated for about 150 degrees F.
Overholser uses only TXL or SXL rated wire, with a cross-linked insulation and a 275 degree F rating. The difference between TXL and SXL is that the insulation on SXL wire is slightly thicker. "The wire with cross-linked insulation won't burn," he says. "It will melt, but won't burn. The PVC stuff will actually burn."
8. Add Spares
He says that when you are stringing wires under the dash and through bulkheads, it is a good idea to add a couple of extra ones, just in case you decide later to add an electric fan or some other accessory that will require power.
"It is a lot easier to have the wires there and not need them than it is to need them and not have them there," he says. "It's also a lot neater to do it all at once instead of adding more wire later."
9. Use Relays
If you do add a cooling fan, wire it in with a relay instead of right off a switch. "The relay will actually make the fan more efficient, so it will cool better," he says.
10. Use Eye Terminals
Overholser prefers eye terminal ends and screws in all his switches. He uses a drop of thread locker on each screw before cinching it tight. Others use liquid electrical tape that is painted on the terminals after everything is installed. A third option is a few drops of waterproof silicone sealer, which not only keeps the screws from backing out but also adds a bit of protection from moisture and dust.
11. Install a Quick-Disconnect Plug
Before actually building a wire harness, decide if you want to include a quick-disconnect plug behind the dash so it can be removed without having to disconnect the gauges and switches. "They aren't too expensive and can make getting to things a lot easier," Overholser says. "If you aren't likely to have to remove the dash to get at stuff behind it, there's probably no good reason to do it."